We have found that only 1 of 5 patients treated with N-acetylprocainamide (NAPA) for 1 year has developed a positive titer of antinuclear antibodies (ANA). This is in marked contrast to experience with procainamide (PA). We plan to extend these observations in the coming year and patients who have positive ANA titers from prior PA therapy will be switched to NAPA to see if their titers fall, or if they are maintained or rise still higher. We hope to study NAPA pharmacokinetics in renal failure patients, and hope that these investigations will provide clues regarding non-renal mechanisms of NAPA elimination. In the coming year we also plan to compare NAPA pharmacokinetics with the kinetics of PVC suppression after intravenous administration of this drug. This should reveal the kinetic identity of the biophase for this drug. In addition, we hope to construct biophase concentration-response curves for NAPA. Finally we will begin physiologic studies in dogs to identify the mechanism by which NAPA exerts its apparent positive inotropic action in patients with chronic PVCs.